In the various analyzing devices, important problems are an improvement of measurement accuracy, an improvement of an inspecting speed, minimization of a specimen and a reagent, and downsizing of a device, and a valve device for controlling a flow rate of a fluid used in measurement is required to be further improved in its performance. Such a valve device employs a diaphragm as a valve opening/closing mechanism in order to realize excellent chemical resistance. The diaphragm forms a bulkhead that divides a valve chest, and receives an external driving force to switch fluid passages.
In this kind of valve device, the housing is provided with one inflow port and two outflow ports so as to communicate with the valve chest. When the diaphragm oscillates, any one of the outflow ports is closed and the other outflow port is opened, and the fluid passages are switched. However, according to elastic deformation of the diaphragm at a time of the passage switching operation, the internal volume of the valve chest changes, and a fluid whose amount corresponds to a variation of the internal volume (pumping volume) is pushed out to the outflow port. For this reason, it is difficult to improve accuracy of the flow rate.
Therefore, conventionally, a method for reducing a membrane portion which controls expansion and contraction of the diaphragm has been examined in order to decrease the pumping volume. However, even if such method is employed, the pumping volume can not be sufficiently decreased. Thus, a method for further decreasing the pumping volume has been demanded. On the other hand, according to the decrease of the membrane portion, a partial expansion/contraction rate of the membrane portion is increased, therefore, a problem occurs such that the life of the diaphragm is shortened. Thus, a new method for decreasing the pumping volume has been sought.
Under the circumstances, the following Patent Literature 1 discloses a valve device in which the area of an inflow port is set to be twice or more of the area of an outflow port.